Subaru WRX 2018 Radio Wiring Schematic Complete Color Coded Guide
Begin by locating the factory harness adapter behind the dashboard’s lower trim panel on the driver’s side. Pinouts for the 20-pin connectors follow this sequence: C1 (constant 12V, red), C2 (switched ignition, yellow), C3 (ground, black), C4-C7 (front/rear speaker outputs, gray, purple, white, green), C8 (illumination, orange). Verify continuity with a multimeter before reconnecting–factory harnesses often apply voltage to unused pins for error suppression.
For amplified systems, bypass the integrated amplifier by splicing into speaker-level inputs at the harness rather than relying on low-level RCA outputs. Use 18-gauge oxygen-free copper wire for all speaker runs to prevent signal degradation. Retain the CAN bus wiring (pins C12-C15, typically blue/white) if retaining steering wheel controls; aftermarket interfaces like Metra ASWC-1 require these connections for full functionality.
Grounding is critical: attach the aftermarket unit’s ground wire directly to the chassis using a dedicated self-tapping screw, not the factory ground point. This prevents noise from shared electrical loads. If retaining the OEM amplifier, expect a 12dB gain–adjust the new unit’s preamp output accordingly to avoid distortion.
For vehicles equipped with navigation or rearview camera inputs, preserve the original wiring for video-in pins (C18-C20, yellow/red). Test camera functionality before finalizing dashboard reassembly–factory camera delay circuits may require a 1-2 second initialization.
Backup all connections with crimp connectors (avoid solder-only joints) and use dielectric grease on all pins to prevent oxidation. Store the factory radio for potential resale or diagnostics; removing it incorrectly can trigger ECU error codes related to entertainment system modules.
Harness Layout for the Premium Audio System in the VA Model Sports Sedan
Locate the OEM harness connector behind the dashboard trim panel on the driver’s side–it’s a 20-pin plug labeled M10. Pin assignments follow this order:
- 1–4: Front left tweeter (+/-) and woofer (+/-)
- 5–8: Front right tweeter (+/-) and woofer (+/-)
- 9–12: Rear left door woofer (+/-) and subwoofer (+/-)
- 13–16: Rear right door woofer (+/-) and subwoofer (+/-)
- 17–18: Antenna power and ground
- 19: Illumination (12V switched)
- 20: Ground (chassis)
For aftermarket head-units use Metra Axxess ASWC-1 adapter; solder directly to pins 17–20 to retain steering-wheel controls without cutting factory harness.
Subwoofer leads (pins 11–12) carry 35W RMS at 2 ohms; verify amplifier impedance matches factory specs before connecting aftermarket amplifier.
Illumination wire (pin 19) dims with dash lights; connect to red wire on new unit if dimming is required–failure will keep display at full brightness.
Ground splice must be direct to chassis at mounting bolt behind climate control module; avoid daisy-chaining to prevent noise.
Test continuity between ground pin (20) and chassis with multimeter reading zero ohms after installation–high resistance causes static during high volume playback.
Use 18-gauge shielded twisted pair for rear-door speaker leads to minimize crosstalk–run separate conduit from front harness through driver-side kick panel.
If upgrading to satellite tuner, tap power from fuse #37 (15A) above glovebox–add fuse tap rated for 20A to prevent tripping during cold starts.
Finding the OEM Cable Bundles Behind the Performance Sedan’s Infotainment Panel
Start by removing the trim surrounding the central console display–grip the lower edge firmly and pull outward with even pressure to release the clips. Behind the screen, two main connectors sit vertically: the upper, larger 24-pin harness (typically white or beige) carries power, CAN bus signals, and speaker outputs, while the smaller 12-pin plug (often black) handles auxiliary inputs like USB and backup camera feeds. Mark each with tape or a marker before disconnecting to avoid mismatching during reinstallation.
Trace the harnesses downward–both terminate into a secondary junction behind the climate controls. The left bundle splits into four branches: constant 12V (red/yellow), switched ignition (red/black), ground (black), and illumination (white). The right grouping includes antenna lead (coaxial), microphone wires (shielded pair), and parking sensors (if equipped). Avoid tugging insulation–use needle-nose pliers to separate tangled wires, particularly the MOST fiber-optic line which requires delicate handling to prevent signal loss.
Before reassembly, verify no stray strands touch bare metal–secure loose cables with zip ties routed through existing factory mounts. If integrating aftermarket components, splice only into designated accessory circuits (e.g., pink/blue for accessory power) rather than CAN bus lines to prevent ECU errors. Test continuity with a multimeter before reconnecting fuses.
Locating Key Connections in Your Vehicle’s Audio Harness
Trace the main power line first–it’s the thickest wire, typically 10-12 gauge, with yellow insulation. This leads directly to the fuse box under the dash on the driver’s side, marked as “IGN” or “ACC” in the owner’s manual schematic. Verify voltage with a multimeter set to DC 20V; readings should jump between 10V and 14V when the ignition cycles. If voltage drops below 9V, inspect the fuse (15A or 20A) and replace if blown–common aftermarket amplifier installations often overload this circuit.
Ground cables cluster near the factory head unit’s mounting bracket. Look for a black wire, often terminated with a ring connector screwed into the chassis. Scrape off paint or coating at the grounding point to ensure conductivity; poor ground causes static, distortion, or intermittent power loss. For verification, connect the multimeter’s negative probe to the battery’s negative terminal and the positive probe to the ground wire–resistance should read below 0.5 ohms. If higher, clean the contact surface with a wire brush and re-secure.
Speaker outputs use a twisted pair per channel, distinguishable by color-coding:
| Channel | Positive (+) | Negative (-) | Typical Gauge |
|---|---|---|---|
| Front Left | White/Black stripe | White | 16-18 AWG |
| Front Right | Gray/Black stripe | Gray | 16-18 AWG |
| Rear Left | Green/Black stripe | Green | 16-18 AWG |
| Rear Right | Violet/Black stripe | Violet | 16-18 AWG |
To confirm polarity, play a 1kHz test tone through each channel and measure AC voltage across the speaker wires–reversing polarity flips the waveform’s phase. Mismatched polarity creates cancellations, reducing bass output by up to 50%. Avoid using solid-state testers for this; they can damage tweeters in premium systems.
Behind the panel, search for a lone purple wire–this is the illumination control, reducing voltage when headlights activate. It regulates dashboard brightness but can interfere with aftermarket units if incorrectly spliced. Connect it only if the new system supports dimming; otherwise, cap it with a 470-ohm resistor to prevent backfeed into the CAN bus. Skipping this step may trigger dash warning lights.
For navigation or satellite modules, locate the teal and red/black wires–these carry MOST bus data and require termination resistors if not connected to compatible hardware. Improper handling disrupts infotainment features like Bluetooth or camera functions. Cutting these wires without a bypass module renders factory telemetry inoperative, requiring a dealer reprogram cycle to reset.
Complete Installation Guide for Upgrading Your Vehicle’s Audio System
Start by disconnecting the negative terminal from the car battery to prevent short circuits during installation. Locate the factory harness behind the dashboard unit–it’s a 20-pin white connector for models with premium sound or a 16-pin grey connector for base systems. Use a multimeter to verify wire functions before cutting or splicing.
Identify the following wires by color and function in the original harness:
- Constant 12V (yellow or orange/black) – Powers memory functions.
- Accessory/Ignition (red or red/white) – Activates the unit with key turn.
- Ground (black or brown) – Ensure solid connection to chassis.
- Front left speaker (+: light blue/black, –: light blue/red) – Polarity matters.
- Front right speaker (+: green/black, –: green/red) – Test before finalizing.
- Rear left speaker (+: violet/black, –: violet/red) – Check for loose strands.
- Rear right speaker (+: gray/black, –: gray/red) – Confirm with tone test.
- Amplifier turn-on (blue/white) – Connects to aftermarket amp relay.
- Illumination (gray) – Dimmer wire for dashboard lights.
- Parking brake (green/white) – Required for video functionality.
- Reverse detection (pink/black) – Triggers backup camera if equipped.
Match the aftermarket stereo’s harness to the vehicle’s connector using a pre-made adapter (Metra 70-8114 or equivalent). If splicing manually, strip 1/4 inch of insulation and twist wires securely. Use heat-shrink tubing or solder for permanent connections–avoid electrical tape alone, as it degrades over time.
For models with steering wheel controls, install an ASWC-1 module. Connect the module’s input wires to the factory switch wires (typically purple and purple/white) and output wires to the stereo’s SWC input. Program the module via short-button press sequences–consult the module’s manual for specific configurations.
Reconnect the battery and test all functions before reassembling the dashboard. Verify:
- Power-on with ignition in ACC and ON positions.
- Speaker balance and fade adjustments.
- Amplifier activation (if applicable).
- Steering wheel control responsiveness.
- Backup camera feed (if installed).
- Dimmer function with dashboard lights.
If static or no sound occurs, recheck ground connections and speaker wire polarity.
Secure all wiring with zip ties, routing cables away from moving parts (e.g., pedals, climate control linkage) and heat sources (e.g., vents, exhaust tunnels). Reinstall dashboard panels carefully–snapping clips improperly can cause rattles or damage trim pieces.
For OEM satellite radio or USB functionality, retain the factory antenna amplifier (small black box behind the glovebox) and connect the aftermarket unit’s satellite input (if compatible). If retaining the original GPS module, splice its TX/RX wires (pink and pink/white) to the new stereo’s navigation harness–consult the stereo’s manual for pin assignments.